U.S. patent application number 15/584357 was filed with the patent office on 2017-12-14 for high optical quality glass tubing and method of making.
The applicant listed for this patent is Corning Incorporated. Invention is credited to David John McEnroe, Aniello Mario Palumbo.
Application Number | 20170355632 15/584357 |
Document ID | / |
Family ID | 60572266 |
Filed Date | 2017-12-14 |
United States Patent
Application |
20170355632 |
Kind Code |
A1 |
McEnroe; David John ; et
al. |
December 14, 2017 |
HIGH OPTICAL QUALITY GLASS TUBING AND METHOD OF MAKING
Abstract
A laminated or single layer glass cylinder and its method of
making are disclosed. The laminated cylinder glass is a precursor
component to enable making subsequent drawn tubing having high
optical quality. The laminated cylinder glass may comprise a first
layer of glass as a clad glass and a second layer of glass as a
core glass. The second layer of glass may be bound to the first
layer of glass. The second layer may have a higher CTE from about
5.times.10.sup.-7/.degree. C. to about 100.times.10.sup.-7/.degree.
C. than the first layer of glass. The first layer and second layer
of glass may have different softening points within about
200.degree. C. of each other. In some embodiments, the first layer
and second layer of glass may have different softening points from
about 50.degree. C. to about 200.degree. C. of each other.
Inventors: |
McEnroe; David John;
(Corning, NY) ; Palumbo; Aniello Mario; (Painted
Post, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated |
Corning |
NY |
US |
|
|
Family ID: |
60572266 |
Appl. No.: |
15/584357 |
Filed: |
May 2, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62348334 |
Jun 10, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02P 40/57 20151101;
C03B 19/04 20130101; C03B 17/025 20130101; C03B 17/04 20130101 |
International
Class: |
C03B 17/04 20060101
C03B017/04; C03B 17/02 20060101 C03B017/02 |
Claims
1. A method for producing a high optical quality hollow cylinder of
glass tubing, comprising: rotating a substantially elongated
tubular mold having a substantially open end at one side, a
substantially closed end at another side, and a cylindrical casting
chamber between the substantially open end and the substantially
closed end, the substantially elongated tubular mold being rotated
along an elongated axis passing through the open end and the closed
end; heating at least a portion of the substantially elongated
tubular mold at or above a strain point temperature
(.eta.=10.sup.14.5 P) of the glass from which the glass tubing is
formed; delivering molten glass via stream or gob through the
substantially open end into the cylindrical casting chamber while
rotating the substantially elongated tubular mold; tilting the
substantially elongated tubular mold to a substantially horizontal
position while rotating the substantially elongated tubular mold;
rotating the substantially elongated tubular mold on a generally
horizontal axis; causing molten glass to assume a form of a
cylindrical tube in response to the rotation of the mold; and
cooling the cylindrical tube of glass to be quenched to form a
first glass cylinder within a range including solidified,
isoviscous or semi-solidified states.
2. The method of claim 1, wherein the substantially elongated
tubular mold is made of at least one of graphite, ceramics,
inconel, platinum or combinations thereof.
3. The method of claim 1, further comprising cleaning the first
glass cylinder by water or acid etching or both, or grinding and
polishing outer surfaces of the first glass cylinder to obtain a
good surface condition with consistent wall thickness.
4. The method of claim 1, wherein the substantially elongated
tubular mold comprises an inner flange adjacent to the open end of
the substantially elongated tubular mold to keep the cylindrical
tube of glass from flowing out of the substantially elongated
tubular mold.
5. The method of claim 1, further comprising redrawing the first
cylinder of glass by feeding the first cylinder of glass into a
down feed system at a feed rate v.sub.f from about 0.2 mm/min to
about 100 mm/min to a heating zone with a heating zone temperature
T.sub.h from about 300.degree. C. to about 1500.degree. C.
corresponding to a viscosity range from about 10.sup.4 P to about
10.sup.7 P.
6. The method of claim 5, further comprising softening the first
cylinder of glass in the heating zone so as to form a softened
region.
7. The method of claim 6, further comprising drawing off a
component strand in a direction of a drawing axis from the softened
region so as to elongate and reduce the size of the cylindrical
tube to form various diameter sizes of a cylindrical tube of glass
and at a drawing rate v.sub.d from about 0.01 m/min to about 100
m/min, wherein the drawing rate, viscosity of glass, and downfeed
rate control the various diameter sizes of the cylindrical
tube.
8. The method of claim 7, wherein the various diameter sizes of the
cylindrical tube have diminished roughness on the surface, wherein
the rms roughness of the inside surface of the cylindrical tube is
from about 5 nanometers to about 20 nanometers.
9. The method of claim 1, wherein the rotating rate is from about
50 rpm to about 750 rpm.
10. The method of claim 1, wherein the cylindrical casting chamber
has a taper from the substantially closed end to the substantially
open end so as to ensure a release of the cylindrical tube.
11. The method of claim 1, further comprising delivering a second
glass of different composition from the first into the mold inside
the first glass cylinder and spinning to make a second concentric
cylinder inside the first.
12. The method of claim 11, further comprising delivering a third
glass of the same or different composition from first into the mold
inside the second glass cylinder and spinning to make a third
concentric cylinder inside the first and second, wherein the glass
composition of the second and the third glass have different
coefficients of thermal expansion.
13. The method of claim 11, wherein the glass composition of the
first and the second glass have different coefficient of thermal
expansion (CTE).
14. The method of claim 12, wherein each of the first and the third
CTE is from about 20.times.10.sup.-7/.degree. C. to about
100.times.10.sup.-7/.degree. C., and the second CTE is from about
25.times.10.sup.-7/.degree. C. to about
120.times.10.sup.-7/.degree. C.
15. The method of claim 11 further comprising removing or reducing
one or more layers of glass via etching mechanical means.
16. A laminated cylindrical glass, comprising: a first layer of
glass as a clad glass; and a second layer of glass as a core glass
bound to the first layer of glass, wherein the second layer has a
higher CTE than the first layer of glass with a CTE difference from
about 5.times.10.sup.-7/.degree. C. to about
100.times.10.sup.-7/.degree. C., wherein the first layer and the
second layer of glass have different compositions and softening
points within about 200.degree. C. of each other.
17. The laminated cylindrical glass of claim 16, further comprising
a third layer of glass bound to the second layer of glass, wherein
the third layer has lower CTE than the second layer of glass.
18. The laminated cylindrical glass of claim 17, wherein the third
layer of glass has a different composition than the second layer
and the same or different composition as the first layer of glass,
and wherein the glass composition of the second and third glass
have different coefficients of thermal expansion.
19. The laminated cylindrical glass of claim 16, wherein the CTE
difference between the first layer and the second layer of glass is
from 5.times.10.sup.-7/.degree. C. to about
50.times.10.sup.-7/.degree. C., or wherein the first layer and the
second layer of glass have different softening points from about
50.degree. C. of each other to about 100.degree. C. of each
other.
20. The laminated cylindrical glass of claim 16, wherein the first
layer and the second layer of glass have different softening points
within about 50.degree. C. of each other.
Description
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119 of U.S. Provisional Application Ser. No.
62/348,334 filed on Jun. 10, 2016, the content of which is relied
upon and incorporated herein by reference in its entirety.
SUMMARY
[0002] The present disclosure relates generally to systems and
methods for making or modifying the shape of a hollow glass
structure, and more particularly to systems and methods for
manufacturing high optical quality glass tubing.
[0003] In one embodiment, the present disclosure teaches a method
for producing hollow cylinder of glass tubing. The method may be
carried out by rotating a substantially elongated tubular mold. The
tubular mold may have a substantially open end at one side, a
substantially closed end at another side, and a cylindrical casting
chamber between the substantially open end and the substantially
closed end. The substantially elongated tubular mold may be rotated
along an elongated axis passing through the open end and the closed
end. At least a portion of the substantially elongated tubular mold
may be heated at or above the strain point temperature
(.eta.=10.sup.14.5 P) of the glass from which the glass tubing is
formed. Molten glass may be delivered via stream or gob through the
substantially open end into the cylindrical casting chamber while
rotating the substantially elongated tubular mold. The
substantially elongated tubular mold may be tilted to a
substantially horizontal position while rotating the substantially
elongated tubular mold. The substantially elongated tubular mold
may be rotated on a generally horizontal axis to cause molten glass
to assume a form of a cylindrical tube in response to the rotation
of the mold. The cylindrical tube of glass may be cooled to be
quenched to form a first glass cylinder within a range including
solidified, isoviscous, or semi-solidified states.
[0004] In another embodiment, a laminated cylinder glass may
comprise a first layer of glass and a second layer of glass. The
first layer of glass may be used as a clad glass. A second layer of
glass may be used as a core glass bound to the first layer of
glass. The second layer may have a higher coefficient of thermal
expansion (CTE) than the first layer of glass with a CTE difference
from about 5.times.10.sup.-7/.degree. C. to about
100.times.10.sup.-7/.degree. C. The first layer and second layer of
glass may have different softening points within about 200.degree.
C. of each other.
[0005] Additional features and advantages of the present disclosure
will be set forth in the detailed description, which follows, and
in part will be readily apparent to those skilled in the art from
that description or recognized by practicing the embodiments
described herein, including the detailed description, the claims,
and the appended drawings.
[0006] It is to be understood that both the foregoing general
description and the following detailed description describe various
embodiments and are intended to provide an overview or framework
for understanding the nature and character of the claimed subject
matter. The accompanying drawings are included to provide a further
understanding of the various embodiments, and are incorporated into
and constitute a part of this specification. The drawings
illustrate the various embodiments described herein, and together
with the description serve to explain the principles and operations
of the claimed subject matter.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0007] The following is a description of the figures in the
accompanying drawings. The figures are not necessarily to scale,
and certain features and certain views of the figures may be shown
exaggerated in scale or in schematic in the interest of clarity or
conciseness.
[0008] FIG. 1a is a cross-sectional view of an elongated tubular
mold according to one embodiment.
[0009] FIG. 1b is a side-view of a rotational caster according to
one embodiment.
[0010] FIG. 1c is a top-view of the rotational caster according to
one embodiment.
[0011] FIG. 2 is a perspective view of a three-layer glass cylinder
according to one embodiment.
[0012] FIG. 3 is a cross-sectional view of a laminated cylindrical
glass with a single core according to another embodiment.
[0013] FIG. 4 is a cross-sectional view of a laminated cylindrical
glass with a dual core according to yet another embodiment.
[0014] The foregoing summary, as well as the following detailed
description of certain inventive techniques, will be better
understood when read in conjunction with the figures. It should be
understood that the claims are not limited to the arrangements and
instrumentality shown in the figures. Furthermore, the appearance
shown in the figures is one of many ornamental appearances that can
be employed to achieve the stated functions of the apparatus.
DETAILED DESCRIPTION
[0015] The present disclosure can be understood more readily by
reference to the following detailed description, drawings,
examples, and claims, and their previous and following description.
However, before the present compositions, articles, devices, and
methods are disclosed and described, it is to be understood that
this disclosure is not limited to the specific compositions,
articles, devices, and methods disclosed unless otherwise
specified, as such can, of course, vary. It is also to be
understood that the terminology used herein is for the purpose of
describing particular aspects only and is not intended to be
limiting.
[0016] The following description of the disclosure is provided as
an enabling teaching of the disclosure in its currently known
embodiments. To this end, those skilled in the relevant art will
recognize and appreciate that many changes can be made to the
various aspects of the disclosure described herein, while still
obtaining the beneficial results of the present disclosure. It will
also be apparent that some of the desired benefits of the present
disclosure can be obtained by selecting some of the features of the
present disclosure without utilizing other features. Accordingly,
those who work in the art will recognize that many modifications
and adaptations to the present disclosure are possible and can even
be desirable in certain circumstances and are a part of the present
disclosure. Thus, the following description is provided as
illustrative of the principles of the present disclosure and not in
limitation thereof.
[0017] Reference will now be made in detail to the present
preferred embodiment(s), examples of which are illustrated in the
accompanying drawings. The use of a particular reference character
in the respective views indicates the same or like parts.
[0018] Unless otherwise indicated, all numbers expressing
quantities of ingredients, properties such as size, weight,
reaction conditions and so forth used in the specification and
claims are to the understood as being modified in all instances by
the term "about". Accordingly, unless indicated to the contrary,
the numerical parameters set forth in the following specification
and attached claims are approximations that may vary depending upon
the desired properties sought to be obtained by the invention. At
the very least, and not as an attempt to limit the application of
the doctrine of equivalents to the scope of the claims, each
numerical parameter should at least be construed in light of the
number of reported significant digits and by applying ordinary
rounding techniques.
[0019] As used herein, the term "about" means that amounts, sizes,
formulations, parameters, and other quantities and characteristics
are not and need not be exact, but may be approximate and/or larger
or smaller, as desired, reflecting tolerances, conversion factors,
rounding off, measurement error and the like, and other factors
known to those of skill in the art. In some embodiments, the term
"about" means plus or minus 10% of the numerical value of the
number with which it is being used. Therefore, about 50% means in
the range of 45%-55%.
[0020] As used herein, "strain point" temperature values means the
temperature at which the glass product has a viscosity of
10.sup.14.5 in units of poise, and is determined in accordance with
a fiber elongation method based on American Society for Testing and
Materials (ASTM) C336-71.
[0021] As used herein, "coefficient of thermal expansion" values
(or CTE values) are determined using an Orton dilatometer in
accordance with ASTM E228-06 over a temperature range of 25.degree.
C. to 300.degree. C.
[0022] Terminology of a short and long glass used herein signifies
that a short glass is a comparative term signifying a fast-setting
glass. Long glass is a comparative term signifying a slow-setting
glass ("The Handbook of Glass Manufacture" Tooley volume II 1974).
A fast setting glass has a steep viscosity curve and will become
solid or more viscous over a shorter time period and lesser
temperature range. A slow-setting glass has a shallow viscosity
curve and will become solid or more viscous over a longer time
period and greater temperature range.
[0023] Broadly, the present disclosure relates to systems and
methods for making or modifying the shape of a hollow glass
structure, and more specifically, to single layer or laminated
cylindrical glass having high optical quality via spin or
rotational casting. The advantage of tube fabrication by rotational
casting is to obtain an optically clear tube free from surface
imperfections created when molten glass is drawn over some type of
forming tools such as an orifice ring, bell or mandrel that exists
with current tubing manufacturing process. The art of this
disclosure is to produce good optical clarity tubing that can be
reshaped into the desired geometry wanted for electronic devices or
other tubular products. A two-step process to fabricate tubing is
done by first rotationally casting large diameter glass cylinders
and then redrawing cylinders into the required tube sizes. Molten
glass is poured into a rotating mold inside a drum that is spun at
high rpms to move the glass against the mold walls by centrifugal
force. The internal glass surface of the cylinders has not touched
any other surface and is therefore pristine. The outside of the
cylinder has come into contact with the mold so it will require
some finishing by grinding and polishing. By making a large
cylinder and then redrawing it into hundreds of feet of smaller
tubing will eliminate the need to grind and polish each individual
tube if high optical clarity is required. The redraw process
enables less stringent tolerances on the cylinder since by
redrawing at certain reduction ratios, the tolerances can be
improved and minor defects in the cylinder are reduced in size to
become insignificant.
[0024] Consumer handheld and wearable electronic manufacturers have
an interest in using all glass body with which to encapsulate their
products. The glass body or sleeve is a three dimensional shape,
currently formed from a starting round tube of glass. Good
geometrical tolerances have been met by reshaping glass tubing, but
one attribute that has eluded this forming process is optical
clarity, especially on the reformed flat surfaces. To obtain good
optical clarity of the sleeve, the initial tubing has to have a
high degree of optical clarity. In-house drawn tubing plus
commercial tubing all show some surface optical perturbations
called paneling. Paneling is a result of molten glass contact with
forming tooling used to make the tubing. The process of using an
orifice ring and internal bell or mandrel over which the glass
flows in order to create a hollow tube causes paneling in the
interior and exterior of the hollow tube. Paneling results because
the viscosity of the molten glass is high enough to allow the
forming tooling to impart longitudinal lines onto the surface of
the resulting tubing as the glass flows over the tooling.
[0025] These longitudinal paneling lines are a series of peaks and
valleys on the tube surface from the glass contact with the metal
tooling. The peaks and valleys are very small on the order of 5 to
100 nanometers and are not highly visible on the round tube. Using
a shadowgraph technique in which a xenon light is shown through the
tubing creating a shadow on a white background, the paneling
becomes apparent. When the tubing is reformed into a sleeve shape,
the flat areas on the sleeve can show paneling especially when
viewing a display through the sleeve wall. The display area is
critical for electronic devices such as phones, watches and other
display related products. A clear optical surface may be required
so no distortions in the display may be observed. If the internal
and external tube surfaces are ground and polished, the paneling
can be reduced or eliminated, but achieving this surface polish is
very difficult timely and costly.
[0026] Generally, three dimensional shaped glass bodies or sleeves
are currently formed by starting with a round tube of glass.
Strengthened and durable tubing is of interest for use for vials or
syringes for pharmaceutical packaging. Current pharmaceutical
vessels are made via using round tubing which is then converted by
flame working the tubing on automated machines. A laminated tube in
both of these applications can provide higher strength and enable
the compositions to be tailored to provide other enhancements like
anti-microbial, durability, color esthetic and hardness. The
advantage of a laminated tube, over other strengthening techniques
like ion exchange, is that creating a deep compressive layer of
glass on the outer surface may provide a glass layer of thickness
equal to that provided by an outer clad glass. Ion exchange
requires long time and higher temperatures to create compressive
stress depths on the order of 100 microns whereas a laminated tube
having an outer layer in compression can be on the order of a
number of millimeters. This is important in manufacturing
environment where containers can bump into each other creating
flaws that can be deeper than the ion exchange depth resulting in
failure of the part.
[0027] The laminated tubing can have two, three or multiple layers
of different glasses depending on the ability to perform the
rotational casting to create a cylinder with many layers. Having
different glasses as discussed above may bring value added
attributes to a single formed tube that cannot exist with a single
composition tube. Making a macro size glass cylinder (such as
laminated cylinder), then redrawing it to a smaller desired tube
size help to reduce any imperfections and obtain greater tolerances
on the final tubing.
[0028] In one embodiment, as shown in FIG. 1, the present
disclosure teaches a method for producing a hollow cylinder of
glass tubing as a precursor preform to make high optical quality
tubing. The method may be carried out by rotating a substantially
elongated tubular mold 100. The tubular mold may have a
substantially open end 110 at one side, a substantially closed end
130 at another side, and a cylindrical casting chamber 150 between
the substantially open end 110 and the substantially closed end
130. The cylindrical casting chamber 150 may be the inside surface
of the tubular mold 100 or may be an insert adapted to fit inside
of the tubular mold. The substantially elongated tubular mold may
be rotated along an elongated axis 170 passing through the
substantially open end 110 and the closed end 130. At least a
portion of the substantially elongated tubular mold may be heated
close to the strain point temperature (.eta.=10.sup.14.5 P) of the
glass from which the glass tubing is formed. Molten glass may be
delivered via stream or gob through the substantially open end 110
into the cylindrical casting chamber 150 while rotating the
substantially elongated tubular mold 100. The substantially
elongated tubular mold 100 may be tilted to a substantially
horizontal position while rotating the substantially elongated
tubular mold 100. The substantially elongated tubular mold 100 may
be rotated on a generally horizontal axis 170 to cause molten glass
to assume a form of a cylindrical tube in response to the rotation
of the mold 100. The cylindrical tube of glass may be cooled to be
quenched to form a first glass cylinder within a range including
solidified, isoviscous or semi-solidified states.
[0029] The substantially elongated tubular mold 100 may be from
about 50 mm to about 500 mm outer diameter, for example, as shown
in FIG. 1b. In one embodiment, the outer diameter may range from
about 100 mm to about 400 mm, for example. In further embodiment,
the outer diameter may be about 200 mm to about 300 mm, for
example. In one embodiment, the length of cylinder may range from
about 250 mm to about 2,000 mm, for example. In another embodiment,
the length of cylinder may range from about 400 mm to about 1,000
mm. In yet another embodiment, the length of cylinder may range
from about 600 mm to about 800 mm. The substantially elongated
tubular mold may be inserted into a rotational drum 20. The drum
may be tilted at various angles to allow the molten glass to flow
in the mold while rotating to achieve more uniform walls. The
rotational drum and the substantially elongated tubular mold 100
are a part of a rotational caster 10. A glass may be melted and
conditioned in a furnace in proximity to the rotational caster 10.
The rotational caster 10 may be mobile, which enables placement
under a melter, and relocation near different furnaces. Glass
viscosity may be important for rotational casting. If the glass is
too viscous (>1000 P), it may not spread out to the mold walls
and may create a thicker wall near the bottom of the cylinder
compared to the top. If the glass is too fluid (<<10 P), it
could form thinner glass walls of the resulting cylinder than
wanted. The overall wall thickness may depend on cylinder diameter,
but a range of wall thickness may include a summation of diameter
layers from about 2 mm to about 50 mm. In another embodiment, the
wall thickness may be from about 5 mm to about 25 mm. In further
another embodiment, the wall thickness may be from about 10 mm to
about 20 mm.
[0030] A quartz glass for instance, would be extremely difficult to
be rotationally cast due to the high temperatures required to
achieve the correct viscosity of the glass (.gtoreq.1900.degree.
C.). Quartz is a very short glass with a steep viscosity curve that
solidifies quickly with loss of temperature.
[0031] A molten glass may be delivered to the rotational caster by
a heated crucible, ladle or flowing directly into the mold 100
seated inside the rotational caster. If a crucible is used to
convey the glass to the rotational caster, it should be preheated
at or above the temperature of the glass in the furnace. The glass
should not be cooled because it will become more viscous as it is
delivered to the rotational caster. Viscosity may range from about
15 P to about 500 P for pouring glass into a rotational mold. In
one embodiment, the viscosity may range from 25 P to about 300 P.
In further embodiment, the viscosity may range from about 50 P to
about 100 P. For example, a soda-lime-silicate glass is melted in a
furnace and conditioned at 1350.degree. C. The glass is then
delivered out of the furnace via a down-comer tube into a preheated
crucible which is heated in a separate furnace to 1500.degree. C.
After the crucible receives the correct volume of glass in it, the
crucible is transported or conveyed by hands or mechanized
equipment to the rotational caster and the molten glass is poured
into the mold. The mold may be made of at least one of graphite,
ceramics, inconel, platinum or combinations thereof. When pouring
the glass into the rotational caster, the rotational caster is
upright in a vertical position in one embodiment. In another
embodiment, the rotational caster is tilted at a certain angle
.alpha. to the horizontal position. The rotational rate that the
glass is started and spun at can be a function of a number of
dependent and/or independent properties. In some cases the
rotational rate that the glass is started and spun at can be a
function of the glass viscosity, glass temperature, method of glass
delivery, mold temperature, mold size and geometry, mold materials,
and glass cooling rates. While pouring the glass, the rotation rate
may be from about 50 rpm to about 750 rpm. In one embodiment, the
rotational rate may be started at approximately 400 rpm. In another
embodiment, the starting rate may be low at the beginning about 100
rpm. As the glass cools and solidifies, the rotation rate may go up
to 400 rpm to have the centrifugal force overcome increased
viscosity. The glass viscosity may be less than 2000 P. In one
embodiment, the viscosity may range from about 50 P to about 2,000
P. In another embodiment, the viscosity may range from about 100 P
to about 1,000 P. In further embodiment, the viscosity may range
from about 200 P to about 500 P. The glass may be spun outward
against the mold walls, preferably made of graphite, with rotation.
In the vertical position, the glass may start to climb up the walls
of the mold due to centrifugal force. If a cylinder is allowed to
form when the caster is in a vertical position, a wall variation is
observed, resulting in the bottom of the cylinder having a much
thicker wall than the top.
[0032] To induce a more uniform wall in the glass cylinder, the
rotational caster is tilted down to a horizontal position. In one
embodiment, the angle .alpha. may range from about 90 degrees to
about 0 degree. In another embodiment, the angle .alpha. may range
from about 60 degrees to about 0 degree. In further another
embodiment, the angle .alpha. may range from about 45 degrees to
about 0 degree. This may allow the glass to flow towards the top of
the cylinder, which can even out the wall thickness. The
substantially elongated tubular mold may comprise an inner flange
152 adjacent to the open end of the substantially elongated tubular
mold to keep the cylindrical tube of glass from flowing out of the
substantially elongated tubular mold while horizontal. The
cylindrical casting chamber may have a taper 154 from the
substantially closed end 130 to the substantially open end 110 so
as to ensure a release of the cylindrical tube. Most tapers usually
may not be more than 5 degrees unless the final shaped glass has a
taper as a part of its shape. Normally a 1 to 2 degree taper may be
sufficient to allow the glass to be released from the mold. For the
cylinder, if too great a taper is present, it may complicate the
redraw process in maintaining geometry of the drawn tubing.
[0033] Optional in any embodiment, the method of producing a hollow
cylinder of glass may further include a step of delivering a second
glass of different composition from the first layer of glass into
the mold inside the first glass cylinder and spinning to make a
second concentric cylinder inside the first. The second glass may
be delivered to the rotational caster by a heated crucible, ladle
or flowed directly into the mold seated inside the rotational
caster. The glass composition of the first and the second layers of
glass may have different coefficient of thermal expansion (CTE).
Optionally in any embodiments, a third glass of the same or
different composition from the first and second layers of glass may
be delivered into the mold inside the second glass cylinder and may
be spun to make a third concentric cylinder inside the first and
second. The second and the third glass may have different
coefficients of thermal expansion. Each of the first and the third
CTE may be from about 20.times.10.sup.-7/.degree. C. to about
100.times.10.sup.-7/.degree. C., and the second CTE may be from
about 25.times.10.sup.-7/.degree. C. to about
120.times.10.sup.-7/.degree. C. A further number of subsequent
glass may be delivered into the mold inside the third glass
cylinder and may be spun into cylinders inside the initial cylinder
of glass.
[0034] The rotation of the glass in the rotational caster may
continue until the glass has set-up and no longer can flow. The
timing may depend on the viscosity curve of the glass, where a
longer glass will take more time to setup than a shorter glass.
Once the glass is solid, the rotational caster is kept horizontal
and the resulting glass cylinder may be slid out of the mold and
transferred into an annealing oven. A graphite mold may act as a
release agent due to the lubricity of the graphite. If alternative
mold materials are used, a release agent such as hexagonal boron
nitride (hBN) may be used. Use of a release agent may probably
emboss a texture onto the outer surface of the cylinder and
subsequent grinding and polishing of the outer surface may be
required. Graphite foil may also be used to assist in releasing the
glass cylinder from the mold.
[0035] The method for producing a high optical quality hollow
cylinder of glass may further include annealing the cylindrical
tube of glass. After annealing, it can then be machined to clean up
the outer surface by grinding and polishing out the surfaces of the
cylindrical tube of glass to obtain a good surface condition with
even wall thickness.
[0036] The method further comprises cleaning the cylindrical tube
of glass by water or acid etching or both. One or more layers of
glass may have a portion of surface removed or the entire glass
layer removed via etching, such as acid etching. HF may be used as
an etching acid. The first glass layer may be a low temperature
glass or soft glass (which may also be called sacrificial glass).
The soft glass or sacrificial glass may be susceptible to etching.
In some embodiments, a laminated cylindrical glass having two or
more layers and having the first layer removed may obtain a
pristine second layer. In cases where there are multiple layers
(such as four layers), the second layer may become the "outer"
layer upon etching the first layer, so CTEs for a strengthened
laminate glass may have to be considered. In most cases, the
etching of the outer layer glass may only remove grinding
contamination or perform an etching polish of the surface. A
surface etching process can also be implemented to reduce the
overall thickness of the cylinder wall or thickness of the inner or
outer clad layer. If a very thin clad layer is required on the
final tube geometry; it could disable or bypass the process to
successfully spin a cylinder with the required thickness especially
if a thin outer clad layer of the cylinder is desired. A post
etching process could remove glass from the interior and or
exterior cylinder walls to reduce the overall thickness of the
layers and after drawing result in thinner clad layers on the
resulting tubing.
[0037] Once the cylinder has been cleaned up by machining with a
possible post acid polishing step, it is ready to redraw into a
final tube geometry. Spending the time and cost on the cylinder may
be made up if good quality tubing of the correct geometry and
optical clarity is achieved. For example, if a 300 mm diameter
cylinder is drawn down to 25 mm tubing, about 150 feet of tubing
may be obtained from one foot of cylinder. It is possible to flame
work/splice several cylinders together to make a longer cylinder
preform. Longer preforms enable drawing multiple cylinders at one
time which improves overall material usage of the cylinders and
produce more tubing for a single draw.
[0038] In one embodiment, a start of the cylindrical tube of glass
may be fed by a down feed system. When redrawing, the cylinder is
placed on the down feed system and slowly lowered into a heated
draw furnace at a feed rate v.sub.f from about 0.2 mm/min to about
100 mm/min to a heating zone with a heating zone temperature
T.sub.h from about 300.degree. C. to about 1500.degree. C.
corresponding to a viscosity range from about 10.sup.4 P to about
10.sup.7 P depending on glass composition. The end of the cylinder
may be heated up and then may be attenuated down in size to make
the final tube size. A component strand in a direction of a drawing
axis may be drawn off from the softened region so as to elongate
and reduce size of cylinder to form various diameter sizes of
cylindrical tube of glass and at a draw rate v.sub.d from about
0.01 m/min to about 100 m/min.
[0039] The drawing rate, viscosity of glass and downfeed rate may
control the various diameter sizes of the drawn cylindrical tube.
The drawing speed may be adjusted by a pulling unit. Reduction
ratios of drawn cylinder can be 2:1 to 2000:1, for example. A
cylinder of 250 mm diameter with a reduction ratio of 2:1 would
form tubing having a 125 mm diameter while 2000:1 tube may be 0.125
mm diameter. Since the inside of the cylinder surface is untouched
or acid etched/polished, it will have a pristine surface and the
outside of the tube being polished may have a panel free surface.
The various diameter sizes of the resulting drawn cylindrical tube
will have diminished (roughness) oscillating peaks and valleys on
the surface. Measurements of roughness can be done using a white
light interferometer, such as the New View 5000 available from Zygo
Corp. The (surface roughness) oscillating peaks and valleys may
average at nanometer levels, such as from about 5 nanometers to
about 20 nanometers. By attenuating the larger cylinder down in
size, any surface defects from polishing may be reduced to an
insignificant size and tighter tolerances on geometry can be gained
on the drawn tubing compared with the cylinder. Reduction ratio of
the draw may reduce defects the same as diameter. If a reduction
ratio of 12.5:1 is used to make 20 mm diameter tube from a 250 mm
diameter cylinder, a defect of 50 nm may now be 4 nm in size and
may be too small to be seen by naked eyes. Tubing tolerances may
also hold true to reduction ratio and a starting tolerance of
+/-1.00 mm on the cylinder may be +/-0.08 mm on the drawn tube.
[0040] Inside surface of a soda-lime tube fabricated via a
traditional down drawing method may have surface roughness of
Ra=0.025 micron (25 nm) and rms=0.058 micron (58 nm). Outside
surface of a soda-lime tube fabricated via a traditional down
drawing method may have surface roughness of Ra=0.026 micron (26
nm) and rms=0.080 micron (80 nm). By using the present spin casting
and down drawing technique, the inside surface of drawn tube has
less surface roughness of Ra=0.341 nm, rms=0.441 nm. Outside
surface of in-house drawn tube has less surface roughness of
Ra=1.312 nm, rms=2.157 nm. The present spin casting and down
drawing technique can significantly improve surface quality as well
as improve strength of glass tube.
[0041] To fabricate a multi-layer laminated cylinder, once the
first glass has set-up and solidified, a second glass may be poured
into the rotational caster. The caster may be positioned back up
into a vertical or angled position and the second glass delivered
inside the first solidified cylinder. The first cylinder of glass
may still be hot enough that contact with the second molten glass
does not thermal shock the glass. Most qualitative in nature is
glass color change as it cools. By the time when all color from
heat leaves from the glass, it becomes close to its strain point.
But if too much time is taken and the first glass is cooled below
its strain point, then cracking could occur. Normally, delivering
the second glass within a few minutes of the already formed first
cylinder being setup may suffice. The process may be repeated
multiple times until a number of layers may be achieved.
[0042] If the fabricated laminate cylinder is redrawn into tubing,
the laminate structure may be maintained since the glass viscosity
is high enough during drawing to prevent the glass layers from
mixing. As shown in FIG. 2, a high optical quality laminated
cylindrical glass 200 may have a first layer of glass 220 and a
second layer of glass 240. The first layer of glass 220 may be used
as a clad glass, such as an outer clad glass. The second layer of
glass 240 may be used as a core glass. The second layer of glass
240 may be bound to the first layer of glass 220.
[0043] The second layer of glass 240 may have a higher CTE than the
first layer of glass 220. The laminated cylindrical glass may
further include a third layer of glass 260 bound to the second
layer of glass 240. The third layer of glass 260 may be used as an
inner clad glass. When considering what glass compositions to
choose from for laminating, several parameters have to be
considered. To create strengthened tubing, a thermal expansion
coefficient on the outer clad glass may have to be less than the
expansion coefficient of the inner core glass. The inner clad glass
may have an expansion coefficient less than the core glass, which
may keep both the inner and outer surface glass in compressional
stress when cooled. The third layer may also have lower CTE than
the first layer of glass. The difference between the thermal
expansions may depend on the compressive stress desired. The CTE
difference between the first layer of glass 220 and the second
layer of glass 240 may be from about 5.times.10.sup.-7/.degree. C.
to about 100.times.10.sup.-7/.degree. C. The first layer of glass
220 and the second layer of glass 240 may have different softening
points from about 50.degree. C. to about 200.degree. C. of each
other. The first layer of glass 220 may have different composition
as the second layer of glass 240. The third layer of glass 260 may
have the same or different composition as the first and second
layers of glass 220.
[0044] As shown in FIG. 3, the second layer of glass 240 as a core
glass may be much thicker than the first layer of glass 220 and the
third layer of glass 260 as clad glass. The third layer of glass
260 may have the same or different composition as the first layer
of glass 220. The glass composition of the second layer of glass
240 and third layer of glass 260 may have different coefficient of
thermal expansion. Geometry of the spun cylinder may take on any
size and wall thickness. For example, a 250 mm diameter cylinder
drawn down to 25 mm tube outer diameter has a reduction ratio of
about 10:1. If the cylinder wall is 20 mm thick, then the resulting
tube wall may be 2 mm thick. This holds the same for the laminated
layer thicknesses corresponding to the resulting thickness of the
tube. If a 200 micron outer clad, 800 micron core and a 200 micron
inner clad is required for the tube, the cylinder may have to have
an outer clad thickness of 2 mm, core 8 mm and inner clad 2 mm.
Therefore, the range of thickness for the cylinder wall is variable
depending on the required tube geometry. A thickness range for a
250 mm diameter cylinder wall would be from about 2 mm to about 50
mm, preferred from about 5 mm to about 35 mm and best from about 10
mm to about 20 mm. This thickness may represent the sum of all the
laminate layers with each individual layer making up some
proportion of the total thickness. If smaller cylinders are formed,
the wall thickness usually is reduced while large cylinders may
have thicker walls. This proportion exists more from a structural
integrity standpoint where it may be difficult to handle a 400 mm
diameter cylinder having only a 2 mm wall thickness. As discussed
previously, many methods, such as a surface etching process, could
be implemented to reduce the overall thickness of the cylinder wall
or thickness of the inner or outer clad layer.
[0045] As shown in FIG. 4, the high optical quality laminated
cylindrical glass 200 may further include a fourth layer of glass
280 bound to the third layer of glass 260. The second layer of
glass 240 and the third layer of glass 260 may be used as dual core
glass.
[0046] As mentioned before, a possible application for laminated
tubing could be pharmaceutical packaging. The need for strong
containment vessels for expensive drugs is straight forward but
having a durable material that impedes leaching or extracting
something into the drug is important especially with the current
concerns with plastics. Three or four layered laminated cylinder
may be tailored to make tubing having a strong hard outer glass to
protect from damage, improved strength for a whole container, and a
durable inner surface impervious to chemicals such as
pharmaceuticals. For a practical use of a laminated tube for
electronic devices that add strength of the laminated glass, a
glass that could be anti-microbial or one that is hard in order to
resist scratches or both may be used.
Example I
[0047] Glass A--CTE 91.times.10.sup.-7/.degree. C. and softening
point--840.degree. C.
[0048] Glass B--CTE 66.times.10.sup.-7/.degree. C. and softening
point--880.degree. C.
[0049] Glass A may be used as a core glass. Glass B may be used as
an outer or inner clad glass. The CTE difference between glass A
and glass B of 25.times.10.sup.-7/.degree. C. may be a good value.
The typical CTE difference range is 5 to
100.times.10.sup.-7/.degree. C. A range of 20 to
50.times.10.sup.-7/.degree. C. may be the best. The softening point
of the glass pairs needs to be within 200.degree. C. of each other.
In some embodiments, the softening point of the glass may be from
about 50.degree. C. to about 200.degree. C. of each other. The
softening point of the glass pairs may be best within 50.degree. C.
If the softening point is too far apart, one glass could remain
viscos while the other is solid. This could deform the cylinder if
extracted hot out of the rotational mold or during redrawing, one
glass could start to draw down but the other is stiff and
unyielding to draw down. A viscosity matched pair of glass is
optimal for any forming processes but some viscosity difference of
+/-1000 P is formable.
[0050] Having described the subject matter of the present
disclosure in detail and by reference to specific embodiments
thereof, it is noted that the various details disclosed herein
should not be taken to imply that these details relate to elements
that are essential components of the various embodiments described
herein, even in cases where a particular element is illustrated in
each of the drawings that accompany the present description. For
example, FIGS. 1-4 are merely a schematic illustration of a
laminated cylindrical glass 200 according to one embodiment of the
present disclosure. A variety of laminated cylindrical glass are
contemplated herein, the structural details of which may be
conveniently gleaned from the present description, the accompanying
drawings, and the appended claims. FIGS. 1-4 are presented for
illustrative purposes and are not intended to create a presumption
that each of the various aspects illustrated therein is a necessary
part of the various embodiments contemplated herein.
[0051] The claims appended hereto should be taken as the sole
representation of the breadth of the present disclosure and the
corresponding scope of the various embodiments described herein.
Further, it will be apparent that modifications and variations are
possible without departing from the scope of the invention defined
in the appended claims. More specifically, although some aspects of
the present disclosure are identified herein as preferred or
particularly advantageous, it is contemplated that the present
disclosure is not necessarily limited to these aspects.
[0052] It is noted that one or more of the following claims utilize
the term "wherein" as a transitional phrase. For the purposes of
defining the present disclosure, it is noted that this term is
introduced in the claims as an open-ended transitional phrase that
is used to introduce a recitation of a series of characteristics of
the structure and should be interpreted in like manner as the more
commonly used open-ended preamble term "comprising."
[0053] It is also noted that recitations herein of "at least one"
component, element, etc., should not be used to create an inference
that the alternative use of the articles "a" or "an" should be
limited to a single component, element, etc.
[0054] It is further noted that recitations herein of a component
of the present disclosure being "configured" in a particular way,
to embody a particular property, or to function in a particular
manner, are structural recitations, as opposed to recitations of
intended use. More specifically, the references herein to the
manner in which a component is "configured" denotes an existing
physical condition of the component and, as such, are to be taken
as a definite recitation of the structural characteristics of the
component.
[0055] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised that do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
* * * * *